LeetCode 1.Two Sum

題目

Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Output: Because nums[0] + nums[1] == 9, we return [0, 1].

解法思維

剛開始是想跑兩個迴圈，跑完再判斷相加是否等於目標值

var twoSum = function(nums, target) {
    for (let i = 0; i < nums.length; i++) {
        for (let j = 1; j < nums.length; j++) {
            if(nums[i]+nums[j]==target){
                return [i,j]
            }
        }
    }
};

別人的想法：跑迴圈，在判斷目標數值與迴圈數值相減，是否有在obj={}裡

var twoSum = function(nums, target) {
    //object for storing value and their index
    const obj = {};
    const len = nums.length;
    for( let i=0; i< len; i++ ){
        //if target - current value in array exist in obj then that's what we need
        if( target - nums[i] in obj ){
            return [ obj[ target - nums[i] ], i ];
        }
        //if target - current value doesn't exist in obj then push the value in obj
        obj[ nums[i] ] = i;
    }
};